There are various reasons for thickening water, aqueous solutions, hydrophilic fluids, and the like, such as for use as water-based metal working fluids, fire control fluids, oil field drilling fluids, food additives, hydraulic fluids, water-based paints or coatings, stripping solutions, and other applications wherein thickening of a liquid or solution is beneficial.
Water thickening agents, such as guar gum and polyacrylamide are not stable to high shear, hydrothermal treatment above about 250.degree. F. (121.degree. C.), oxidation, bacterial attack, and salts. To make up for some of these problems, such additives as bacteriacides and antioxidants are sometimes required.
Thickening agents or viscosifying agents for aqueous materials, such as drilling fluids, which involve some form of hydrous aluminum compound are disclosed, for example, in U.S. Pat. Nos. 4,240,915, 4,349,443, 4,366,070, 4,389,319, 4,428,845, 4,431,550, 4,447,341, 4,473,479, and 4,486,318. Patents disclosing other forms of aluminum compounds for the same purpose are, e.g., U.S. Pat. Nos. 4,240,924, 4,353,804, 4,411,800, and 4,473,480. Similar patents disclosing other types of viscosifying agents are, e.g., U.S. Pat. Nos. 4,255,268, 4,264,455, 4,312,765, 4,363,736, and 4,474,667.
These patents deal with the formation of the hydrous aluminum compounds in-situ. The major disadvantages to such a process are: (1) The resulting thickened fluid contains copious amounts of reaction salts. This may be undesirable in many situations. For example, in applications such as paints, metal working fluids, or water-based hydraulic fluids, the presence of salt could cause severe corrosion problems. In the case of oil field drilling fluids, many performance additives do not work well if salt is present. Thus it is desirable to drill in fresh water if possible. (2) The reactions described in the cited patents are run in-situ (e.g. in the mud pit of a drilling rig); under such conditions the reaction cannot be adequately controlled and the properties of the resultant thickener may be unpredictable.
Other problems with the use of Al(OH).sub.3 as a gelling agent for processes such as oilfield drilling fluids are as follows:
1. Al(OH).sub.3 gels are known to detrimentally change with time unless certain anions such as carbonate or citrate are present.
2. The rheology of Al(OH).sub.3 is not very constant with changing pH values. For example, a slurry of Al(OH).sub.3 may be very thick and uniform at pH 6 but at pH 10, which the drilling industry prefers, the slurry collapses and the Al(OH).sub.3 settles out of suspension. This creates significant problems since most drilling operations are run at pH values in the range of 9 to 10.5.
A historically popular thickening agent, especially in drilling mud, has been mineral clays, such as bentonite clay, often used with other agents or densifiers, such as Fe.sub.2 O.sub.3, BaSO.sub.4 and others. Variations from batch to batch of bentonite clay, and sensitivities to ions and temperature have resulted in erratic results and adjustment of the formulation is often required during use; this hampers the drilling operation.
Certain forms of crystalline layered mixed metal hydroxides are disclosed, e.g., in U.S. Pat. Nos. 4,477,367, 4,446,201, and 4,392,979, wherein various Li, Mg, Cu, Zn, Mn, Fe, Co, and Ni compounds form part of the crystal structure. Other layered compounds are disclosed, e.g., in U.S. Pat. Nos. 2,395,931, 2,413,184, 3,300277, and 3,567,472. These compounds are prepared through various reactions including coprecipitations, intercalations, acid digestions and base digestions.
In the drilling of oil wells, drilling fluids or "muds" perform several functions:
1. They remove cuttings from the hole.
2. They cool the drill bit.
3. They provide hydrostatic pressure to balance formation pressure.
4. They control ingress of fluids into the formation and protect the formation.
In order to perform some of these functions it is necessary for the fluid to possess pseudoplastic rheology. There are several shear zones in the bore hole of a well and the fluid should have varying viscosities in these zones. In the annulus between the drill pipe and the formation, the shear rate is approximately 100 to 1000 sec.sup.-1. At the drill bit the shear rate is between about 25,000 and 200,000 sec.sup.-1. In the mud pit the shear rate is less than 30 sec.sup.-1. In order to carry drill solids at low shear rates, a fluid must have a significant viscosity. However, if the fluid has a high viscosity at the drill bit, a significant amount of energy is lost in pumping the fluid. Thus, a good drilling fluid should be shear thinning. It is very important that the fluid maintain this rheology throughout the drilling process. However, many adverse conditions that typically inhibit the performance of existing drilling fluids are, the presence of various cations (such as calcium and magnesium), fluctuating salt concentrations, high temperatures, oxidative conditions, and the presence of bacteria.
Some of the commercially accepted gelling agents that are used in water-based drilling fluids are polymers such as xanthan gum, guar gum and polyacrylamides. Nonpolymer gelling agents are typically clays such as bentonite and attapulgite. Each of these gelling agents has its own limitations. The polymers typically have instability to various salts, they are susceptible to oxidation and bacterial attack, they break down under extensive shear, and they are thermally stable to only about 120.degree. to 150.degree. C. The most popular clay gelling agent is bentonite. This material is severely affected by polyvalent cations and is limited to about 100.degree. C. unless certain thinners are incorporated. However, bentonite cannot be oxidized under hydrothermal conditions, and it is stable in a liquid carrier to high shear conditions.